In prior studies, our lab found that costs of resistance to pathogens in the absence of disease was ~5-10% for the resistance (R) genes Rps5 and Rpm1, respectively. However, Arabidopsis thaliana has 149 R-genes so it is unlikely that many R genes incur such a high cost. The now published research of former PhD student Alice MacQueen focuses on Rps2 that exists as an ancient balanced polymorphism with two long-lived clades of alleles. Alice conducted field trials that show that Arabidopsis thaliana plants with resistant Rps2 are no less fit than those with a susceptible Rps2 allele in the absence of disease. Both resistant and susceptible Rps2 alleles contribute to controlling defense and stress gene expression thus presenting a pleiotropic effect to explain the maintenance of both alleles.

“These results demonstrate how profoundly the magnitude of fitness costs associated with disease resistance may be shaped by genomic architecture and pleiotropy… These findings shed much-needed light on how the full repertoire of R genes is maintained in the A. thaliana genome. More broadly, these results show that the nature of fitness costs and trade-offs of disease resistance vary among loci even within the same host. Such information is crucial for crop breeding, where the challenge lies in producing high-yield crops while minimizing the cost of disease control.”

We illustrated this post with Sir John Tenniel’s drawing of the Red Queen and Alice from Lewis Carroll’s Through the Looking-Glass. The Red Queen tells Alice: “Now, here, you see, it takes all the running you can do, to keep in the same place”. This is commonly used as an analogy for co-evolution, as hosts and parasites have to rapidly adapt to each other in order to not loose the race. A concept introduced by Leigh Van Valen’s 1973 article. The rate of this co-evolutionary arms race is expected to be constrained by fitness costs.

Alice MacQueen performed fitness experiments as part of her doctoral dissertation and is now a post doctoral researcher with the Juenger lab in Austin Texas.

Xiaoqin Sun worked with the Bergelson lab from 2007-2009 and is now at the Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing.